Since man first began using heted liquids such as water for domestic and commercial purposes, he has had problems, first in heating the liquid and secondly in storing it once heated until it is used.
Before the advent of electric and gas fired heating means, pipes were disposed within a wood or coal stove or fire box and the water or other liquid pumped therefrom into an uninsulated tank. The heat loss and inefficiency of these systems were great and such inefficiency cannot be tolerated in the modern environment.
In more recent times, various methods have been used for heavily insulating tanks or reservoirs for storing heated liquids. These systems have been constructed of various materials and have been formed in various configurations. In many instances, pumps, solenoids, thermostats and other controls have been mounted within an exterior shell for aesthetic purposes. It has always been though necessary, however, to locate these controls exteriorly of the insulated portion of the reservoir for more ready access and also for heat dissipation purposes. Also, vents to allow atmospheric pressure equilibrium in nonpressurized applications have been vented directly to the exterior of the tank with resultant loss of not only heat but of liquid through evaporation.